Free Practice Questions for Juniper JN0-351 Exam

IS-IS (Intermediate System to Intermediate System) is a routing protocol that is designed to move information efficiently within a computer network 1 2 .  It supports multiple protocol topologies, including IPv4, IPv6, and multicast 1 2 . Therefore, options C, E, and D are correct.

A  is correct because you need to configure BGP multihop to enable redundancy for the EBGP peering between the two routers.  BGP multihop is a feature that allows BGP peers to establish a session over multiple hops, instead of requiring them to be directly connected 1 .  By default, EBGP peers use a time-to-live (TTL) value of 1 for their packets, which means that they can only reach adjacent neighbors 1 .  However, if you configure BGP multihop with a higher TTL value, you can allow EBGP peers to communicate over multiple routers in between 1 . This can provide redundancy in case of a link failure or a router failure between the EBGP peers.

B  is correct because you need to configure loopback interface peering to enable redundancy for the EBGP peering between the two routers.  Loopback interface peering is a technique that uses loopback interfaces as the source and destination addresses for BGP sessions, instead of physical interfaces 2 .  Loopback interfaces are virtual interfaces that are always up and reachable as long as the router is operational 2 .  By using loopback interface peering, you can avoid the dependency on a single physical interface or link for the BGP session, and use multiple paths to reach the loopback address of the peer 2 . This can provide redundancy and load balancing for the EBGP peering.

C  is correct because you need to configure routes for the peer loopback interface IP addresses to enable redundancy for the EBGP peering between the two routers.  Routes for the peer loopback interface IP addresses are necessary to ensure that the routers can reach each other’s loopback addresses over multiple hops 2 .  You can use static routes or dynamic routing protocols to advertise and learn the routes for the peer loopback interface IP addresses 2 . Without these routes, the routers will not be able to establish or maintain the BGP session using their loopback interfaces.

A  is correct because RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch.  An alternate port is a backup port for a root port, which means it receives better BPDUs from another bridge than the current root port 1 .  However, an alternate port does not forward any traffic, as it is in a discarding state 2 . It only listens to BPDUs and waits for the root port to fail.  If the root port fails, the alternate port can immediately transition to a forwarding state and become the new root port 1 .

C  is correct because RSTP alternate ports provide an alternate higher cost path to the root bridge.  An alternate port is selected based on the same criteria as the root port, which are the lowest bridge ID, the lowest path cost, the lowest sender port ID, and the lowest receiver port ID 3 .  However, an alternate port receives a higher cost BPDU than the root port, otherwise it would be the root port itself 1 . Therefore, an alternate port provides an alternate higher cost path to the root bridge than the root port.

The default MAC age-out timer on an EX Series switch is 300 seconds 1 2 .  The MAC age-out timer is the maximum time that an entry can remain in the MAC table before it “ages out,” or is removed 3 1 .  This configuration can influence efficiency of network resource use by affecting the amount of traffic that is flooded to all interfaces 1 .  When traffic is received for MAC addresses no longer in the Ethernet routing table, the router floods the traffic to all interfaces 1 .

The two reasons for the failure to form an adjacency in a network running IS-IS could be:

B. There is no configured ISO address on any IS-IS interface. IS-IS requires each router interface to have an ISO address configured.  Without this address, the routers cannot form an adjacency 1 .

D. The family iso configuration is missing from the adjacency interface. The ‘family iso’ configuration is essential for IS-IS to function correctly.  If this configuration is missing from the adjacency interface, it could prevent the formation of an adjacency 1 .

These explanations are based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks 2 3 .

Option A is correct.  The storm control feature is enabled in the factory-default configuration on EX Series switches 1 2 .  On EX2200, EX3200, EX3300, EX4200, and EX6200 switches, the factory default configuration enables storm control for broadcast and unknown unicast traffic on all switch interfaces 2 .  On EX4300 switches, the factory default configuration enables storm control on all Layer 2 switch interfaces 1 .

Option B is incorrect.  The storm control feature does not require a special license on EX Series switches 3 4 .

Option C is incorrect. There’s no information available that suggests the storm control feature is not supported on aggregate Ethernet interfaces.

Option D is incorrect.  The storm control configuration applies to traffic at the ingress of an interface 5 , not just between the forwarding and control plane.

B  is correct because duplex and speed settings are required to match on both participating devices.  According to the Juniper Networks documentation 1 , all the interfaces in a LAG must have the same speed and be in full-duplex mode. This ensures that the LAG can operate as a single logical link without any performance or compatibility issues.

C  is correct because member links are not required to be contiguous ports.  According to the Juniper Networks documentation 2 , you can group any Ethernet interfaces on a switch into a LAG, regardless of their physical location or slot number. This provides flexibility and scalability for configuring LAGs on switches.

According to the OSPF protocol, the designated router (DR) is the router that acts as the focal point for exchanging routing information on a multi-access network segment, such as a LAN 1 .  The DR election process is based on the following criteria, in order of precedence 1 :

The router with the highest OSPF priority becomes the DR. The default priority is 1, and a priority of 0 means the router will not participate in the election.

If there is a tie in priority, the router with the highest router ID becomes the DR. The router ID is a 32-bit number that uniquely identifies a router in an OSPF domain. It can be manually configured or automatically derived from the highest IP address of a loopback interface or a physical interface.

If there is a tie in router ID, the router that was first to become an OSPF neighbor becomes the DR.

In your scenario, two routers share the same highest priority and start time. This means that they have equal chances of becoming the DR based on the first and third criteria. Therefore, the second criterion will be used to break the tie, which is the router ID.  The router with the highest router ID will become the DR, and the other router will become the backup designated router (BDR), which is ready to take over the role of DR if it fails 1 .